COS 258-1 - CANCELLED - Landscape patterns of burn severity and early post-fire forest trajectories in an infrequent and severe fire regime of Western Cascadia

Background/Question/Methods

Understanding the mechanisms that underpin forest resilience to fires is of high importance as the climate warms and fire activity increases worldwide. This knowledge gap is particularly wide in forests characterized by infrequent and severe fires, since opportunities to study fire events are inherently rare. In a series of associated projects, we characterize factors associated with, and indicators of forest resilience to fire west of the Cascade Crest in Washington and northern Oregon, USA (‘western Cascadia’). Using satellite burn severity mapping and landscape ecological analyses, we characterize patterns and drivers of stand-replacing fire from 1984 to 2020, building an understanding of the spatial signature of the western Cascadia fire regime. In a network of intensively measured permanent field plots distributed across forests burned between 2015 and 2020, we measure how pre-fire forest structure, burn severity, and topoclimate relate to several key post-fire indicators of resilience. Specifically, data on post-fire tree regeneration, early-seral vegetation communities, woody carbon, and fuel profiles are critical early indicators of resilience and potential long-term post-fire trajectories.

Results/Conclusions

Landscape patterns of burn severity from 1984 to 2020 were characterized by approximately 50% of area burned occurring as severe, or stand-replacing fire. Although more than 75% of stand-replacing patches were smaller than 1 hectare in size, collectively those small patches accounted for less than 1% of total stand-replacing fire. Conversely, 12 patches of stand-replacing fire that were larger than 1,000 ha in size accounted for >70% of total stand-replacing burned area. Burn severity was a strong predictor of several post-fire indicators of resilience (tree regeneration, plant communities, fuel profiles, and woody carbon), and interacted with pre-fire stand structure (seral stage) to produce a wide range of post-fire successional trajectories. Collectively, findings provide valuable insights into the role that fire plays in shaping western Cascadia, and provide the foundation for understanding resilience to fire now and in the future.